fix(3742): change getMetaMetricsId to only sync func type (#5108)

## Explanation
Changes introduced in this PR including:

- remove fallback of metaMetricsId and rely on client side always
returning a value
- refactor getMetaMetricsId to only handle synchronous (extension)
function

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## References
Addressed feedback
#5051 (comment)
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* Related to #67890
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### `@metamask/remote-feature-flag-controller`

- **CHANGED**: Modify signature of `getMetaMetricsId` to handle only
synchronous function
- **CHANGED**:  Remove fallback of `metaMetricsId`

## Checklist

- [x] I've updated the test suite for new or updated code as appropriate
- [x] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [x] I've highlighted breaking changes using the "BREAKING" category
above as appropriate
- [x] I've prepared draft pull requests for clients and consumer
packages to resolve any breaking changes

packages/remote-feature-flag-controller/src/remote-feature-flag-controller.test.ts

@@ -14,7 +14,6 @@ import type {
   RemoteFeatureFlagControllerStateChangeEvent,
 } from './remote-feature-flag-controller';
 import type { FeatureFlags } from './remote-feature-flag-controller-types';
-import * as userSegmentationUtils from './utils/user-segmentation-utils';
 
 const MOCK_FLAGS: FeatureFlags = {
   feature1: true,
@@ -42,7 +41,6 @@ const MOCK_FLAGS_WITH_THRESHOLD = {
 };
 
 const MOCK_METRICS_ID = 'f9e8d7c6-b5a4-4210-9876-543210fedcba';
-const MOCK_METRICS_ID_2 = '987fcdeb-51a2-4c4b-9876-543210fedcba';
 
 /**
  * Creates a controller instance with default parameters for testing
@@ -59,7 +57,7 @@ function createController(
     state: Partial<RemoteFeatureFlagControllerState>;
     clientConfigApiService: AbstractClientConfigApiService;
     disabled: boolean;
-    getMetaMetricsId: Promise<string | undefined>;
+    getMetaMetricsId: () => string;
   }> = {},
 ) {
   return new RemoteFeatureFlagController({
@@ -68,7 +66,7 @@ function createController(
     clientConfigApiService:
       options.clientConfigApiService ?? buildClientConfigApiService(),
     disabled: options.disabled,
-    getMetaMetricsId: options.getMetaMetricsId,
+    getMetaMetricsId: options.getMetaMetricsId ?? (() => MOCK_METRICS_ID),
   });
 }
 
@@ -271,7 +269,7 @@ describe('RemoteFeatureFlagController', () => {
       });
       const controller = createController({
         clientConfigApiService,
-        getMetaMetricsId: Promise.resolve(MOCK_METRICS_ID),
+        getMetaMetricsId: () => MOCK_METRICS_ID,
       });
       await controller.updateRemoteFeatureFlags();
 
@@ -289,34 +287,14 @@ describe('RemoteFeatureFlagController', () => {
       });
       const controller = createController({
         clientConfigApiService,
-        getMetaMetricsId: Promise.resolve(MOCK_METRICS_ID),
+        getMetaMetricsId: () => MOCK_METRICS_ID,
       });
       await controller.updateRemoteFeatureFlags();
 
       const { testFlagForThreshold, ...nonThresholdFlags } =
         controller.state.remoteFeatureFlags;
       expect(nonThresholdFlags).toStrictEqual(MOCK_FLAGS);
     });
-
-    it('uses a fallback metaMetricsId if none is provided', async () => {
-      jest
-        .spyOn(userSegmentationUtils, 'generateFallbackMetaMetricsId')
-        .mockReturnValue(MOCK_METRICS_ID_2);
-      const clientConfigApiService = buildClientConfigApiService({
-        remoteFeatureFlags: MOCK_FLAGS_WITH_THRESHOLD,
-      });
-      const controller = createController({
-        clientConfigApiService,
-      });
-      await controller.updateRemoteFeatureFlags();
-
-      expect(
-        controller.state.remoteFeatureFlags.testFlagForThreshold,
-      ).toStrictEqual({
-        name: 'groupA',
-        value: 'valueA',
-      });
-    });
   });
 
   describe('enable and disable', () => {

packages/remote-feature-flag-controller/src/remote-feature-flag-controller.ts

@@ -14,7 +14,6 @@ import type {
 import {
   generateDeterministicRandomNumber,
   isFeatureFlagWithScopeValue,
-  generateFallbackMetaMetricsId,
 } from './utils/user-segmentation-utils';
 
 // === GENERAL ===
@@ -103,7 +102,7 @@ export class RemoteFeatureFlagController extends BaseController<
 
   #inProgressFlagUpdate?: Promise<ServiceResponse>;
 
-  #getMetaMetricsId?: Promise<string | undefined>;
+  #getMetaMetricsId: () => string;
 
   /**
    * Constructs a new RemoteFeatureFlagController instance.
@@ -114,7 +113,7 @@ export class RemoteFeatureFlagController extends BaseController<
    * @param options.clientConfigApiService - The service instance to fetch remote feature flags.
    * @param options.fetchInterval - The interval in milliseconds before cached flags expire. Defaults to 1 day.
    * @param options.disabled - Determines if the controller should be disabled initially. Defaults to false.
-   * @param options.getMetaMetricsId - Promise that resolves to a metaMetricsId.
+   * @param options.getMetaMetricsId - Returns metaMetricsId.
    */
   constructor({
     messenger,
@@ -127,7 +126,7 @@ export class RemoteFeatureFlagController extends BaseController<
     messenger: RemoteFeatureFlagControllerMessenger;
     state?: Partial<RemoteFeatureFlagControllerState>;
     clientConfigApiService: AbstractClientConfigApiService;
-    getMetaMetricsId?: Promise<string | undefined>;
+    getMetaMetricsId: () => string;
     fetchInterval?: number;
     disabled?: boolean;
   }) {
@@ -209,8 +208,7 @@ export class RemoteFeatureFlagController extends BaseController<
     remoteFeatureFlags: FeatureFlags,
   ): Promise<FeatureFlags> {
     const processedRemoteFeatureFlags: FeatureFlags = {};
-    const metaMetricsId =
-      (await this.#getMetaMetricsId) || generateFallbackMetaMetricsId();
+    const metaMetricsId = this.#getMetaMetricsId();
     const thresholdValue = generateDeterministicRandomNumber(metaMetricsId);
 
     for (const [

packages/remote-feature-flag-controller/src/utils/user-segmentation-utils.test.ts

@@ -1,9 +1,6 @@
-import { validate as uuidValidate, version as uuidVersion } from 'uuid';
-
 import {
   generateDeterministicRandomNumber,
   isFeatureFlagWithScopeValue,
-  generateFallbackMetaMetricsId,
 } from './user-segmentation-utils';
 
 const MOCK_METRICS_IDS = [
@@ -75,12 +72,4 @@ describe('user-segmentation-utils', () => {
       ).toBe(false);
     });
   });
-
-  describe('generateFallbackMetaMetricsId', () => {
-    it('returns a valid uuidv4', () => {
-      const result = generateFallbackMetaMetricsId();
-      expect(uuidValidate(result)).toBe(true);
-      expect(uuidVersion(result)).toBe(4);
-    });
-  });
 });

packages/remote-feature-flag-controller/src/utils/user-segmentation-utils.ts

@@ -1,5 +1,4 @@
 import type { Json } from '@metamask/utils';
-import { v4 as uuidV4 } from 'uuid';
 
 import type { FeatureFlagScopeValue } from '../remote-feature-flag-controller-types';
 
@@ -39,11 +38,3 @@ export const isFeatureFlagWithScopeValue = (
     'scope' in featureFlag
   );
 };
-
-/**
- * Generates UUIDv4 as a fallback metaMetricsId
- * @returns A UUIDv4 string
- */
-export function generateFallbackMetaMetricsId(): string {
-  return uuidV4();
-}